A technique for converting a base band signal (hereinafter referred to as “BB signal”) or an intermediate frequency signal (hereinafter referred to as “IF signal”) to a radio frequency signal (hereinafter referred to as “RF signal”) using an IQ mixer or a technique for converting the RF signal to the BB signal or the IF signal is widely used in a field of a wireless communication.
However, an IQ imbalance occurs in a real IQ mixer. The IQ imbalance can include a gain imbalance that occurs because amplitudes of an in-phase signal and a quadrature signal transmitted from a local oscillator to the IQ mixer are not identical, and a phase imbalance that occurs because the in-phase signal and the quadrature signal do not have a phase difference of 90°. When the IQ imbalance occurs, an output of the IQ mixer includes an undesirable noise component, which can result in a degradation of a signal-to-noise ratio.
U.S. Pat. No. 5,949,821 by Shahriar Emami titled “METHOD AND APPARATUS FOR CORRECTING PHASE AND GAIN IMBALANCES BETWEEN IN-PHASE (I) AND QUADRATURE (Q) COMPONENTS OF A RECEIVED SIGNAL BASED ON A DETERMINATION OF PEAK AMPLITUDES” and U.S. Pat. No. 6,044,112 by Johua L. Koslov titled “METHOD AND APPARATUS FOR CORRECTING AMPLITUDE AND PHASE IMBALANCES IN DEMODULATORS” disclose related art methods for compensating for IQ imbalance. The patents disclose methods for measuring the IQ imbalance using a received signal transmitted through a wireless communication. However, since IQ imbalance is measured using the received signal in accordance with the method disclosed by the patents, an accuracy of the measured IQ imbalance is degraded because of noise of a wireless channel included in the received signal.
U.S. Pat. No. 7,151,917 by Tod Paulus titled “APPARATUS AND METHOD FOR DERIVING A DIGITAL IMAGE CORRECTION FACTOR IN A RECEIVER” discloses another related art for compensating for an IQ imbalance. In accordance with the patent, a method for measuring the IQ imbalance by inputting a test signal to an IQ down-conversion mixer. However, the technique disclosed by the patent requires a separate test signal and/or does not disclose a Tx IQ.